Flexible waveguide



J. F. ZALESKI FLEXIBLE WAVEGUIDE Aug. 14, 1956 2 Sheets-Sheet 1 Filed Oct. 30, 1953 INVENTOR. L/o/m/ f Z/JZ ES/f/ BY ATTUAA/EV 14, 1956 J. F. ZALESKI 2,158,612

FLEXIBLE WAVEGUIDE Filed Oct. 30, 1953 2 Sheets-Sheet 2 HII, I'll:

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gins 1]. W W :61 W s /0m /7' ZAL/SS/f/ 'IH'IH MM. $21M! 1 Z ATTOEA/EV United States Patent FLEXIBLE WAVEGUIDE John F. Zaleski, Thornwood, N. Y., assignor to General Precision Laboratory Incorporated, a corporation of New York Application October 30, 1953, Serial No. 389,271

4 Claims. (Cl. 138-50) This invention relates generally to hollow waveguides for the propagation of microwave energy and particularly to an improved flexible waveguide section.

In the art of the transmission of microwave energy, there is frequently a need for a flexible waveguide section for joining two relatively moveable components. A flexible section for this purpose should provide the maximum amount of, flexibility for a given length of section. Thesection should have a low voltage standing wave ratio which should remain substantially constant as the waveguide section is flexed. There are frequently imposed the further requirements that the interior of the section be pressurized and that satisfactory operation be obtained although the guide be subjected to wide variations in ambient temperature.

A number of types of flexible waveguide sections are well known. One type comprises a number of discrete conductive elements held closely adjacent by means of a flexible material such as rubber. A second type comprises interlocked conductive elements. A third type comprises a conductive helical corrugation formed into a hollow tube. All of these types of guide require an airtight flexible jacket, such as a rubber jacket, if they are to be pressurized. Such a jacket unduly increases the force necessary to flex the guide, and at low temperatures the jacket may become brittle.

Another known type of flexible waveguide comprises a seamless corrugated tube, similar toa bellows. Such a guide is quite flexible and may readily be pressurized. However, it tends to bend most at its weakest point. The abrupt electrical discontinuities efiected by the small radius of the bend at the weak point causes a large increase in the voltage standing wave ratio.

Correspondingly, the phase of the reflector will be changing very rapidly with flexing. Furthermore, repeated flexing leads to an early mechanical failure at the weak point. All these conditions are to be avoided'if possible.

It is an object of this invention to provide a flexible waveguide section which overcomes the above mentioned disadvantages of prior known flexible sections.

Another object of this invention is to provide a flexible waveguide section suitable for pressurized use which will perform satisfactorily although subjected to a wide range of ambient temperatures.

Another object of the invention is to provide a flexible waveguide section which requires but a moderate force for flexing.

Another object of the invention is to provide a flexible waveguide section with a substantially constant voltage standing wave ratio throughout its range of flexure.

Another object of the invention is to provide a flexible waveguide section with a minimum of electrical phase shift incidental to flexing.

Another object of the invention is to provide a flexible waveguide section having a long life.

In accordance with'the invention, the basic portion of the waveguideis a seamless corrugated tube. A thin strip of resilient metal is laid along one outer face of the guide and loosely secured thereto. When the guide and strip are flexed, the strip will assume a smooth curved form which is very nearly an arc of a circle the radius of which decreases as flexing is increased. One face of the strip bears against one face of the guide, constraining the guide to assume the same smooth curve. Since there are no sharp bends, the voltage standing wave ratio remains substantially'constant. Similarly there are no abrupt phase changes. The tendency of the guide to bend most at its weakest point is eliminated.

For a better understanding of the invention, reference may be made to the accompanying drawing in which.

Figures 1 and 2 are schematic diagrams illustrating the basic concept of the invention;

Figure 3 is an isometric view of a flexible waveguide section incorporating the invention;

Figure 4 is a sectional View of a detail taken along the line 4-4 of Fig. 3;

Figure 5 is another sectional view of a detail taken along the line 5-5 of Fig. 3;

Figure 6, Figures 7 and 8, and Figure 9 are plan views illustrating other means for fastening the resilient plates shown in Fig. 3.

Referring first to Fig. 1, there is shown schematically a cross section of a corrugated waveguide A. Along the outside of the guide there is placed a resilient member B, such as a flat metal strip. If the guide and strip be held loosely together so that longitudinal slipping is possible, the assembly can be flexed as shown in Fig. 2. The strip B will tend to bend in the form of an arc of a circle, and the guide A will follow this curve. It is obvious that a second strip along the bottom of guide 12 would improve the results.

To construct a useful device in accordance with the teachings of Figs. 1 and 2, it is necessary to devise suitable apparatus for holding the strip B in contact with the face of the guide A while permitting slippage between the two. This apparatus may take many different forms, some of which will be particularly described in connection with the remaining figures of the drawing.

Referring now to Fig. 3, there is shown a flexible waveguide section constructed in accordance with the invention. The main body of the waveguide comprises a seamless corrugated rectangular tube 11. Flanges 12 and 13 are secured to opposite ends of the tube 11 to enable this section to be coupled to other microwave components. A thin metal strip 14, approximately the width of the broad face of the tube 11 and slightly shorter, is laid along the top of the tube 11. A similar strip 15 is laid on top of the strip 14. The strip 15 is fastened to the flange 13 in any desired manner. For example, the strip 15 may have an upturned portion 16 which in turn has two laterally extending portions 17 and 18. The

portions 16, 17 and 18 are cut to conform to the shape of the flange 13. The laterally extending portions 17 and 18 are provided with holes 19 and 21 which are in register with similar holes in the flange 13. By this arrangement, when the section is joined to another microwave component by means of av mating flange, the strip 15 is held securely to the flange 13. The strip 14 may have a similar upturned portion and be similarly secured to the flange 12.

The strips 14 and 15 are shown greatly enlarged in thickness in the drawing in order to show their construction more clearly. Actually, the strips 14 and 15 are For example, they may be strips of beryllium copper, Phosphor bronze, or steel leaves .005"

much thinner.

to .015 in thickness.

The strips 14 and 15 are fastened together by means of a pair of loose fitting rivets 22 and 23. As shown more clearly inFigs. '4 and 5, the strip14 has a hole 24 punched in it. The'edges of the hOIBhfiVCUPtUIIlCdPOI'flOflS 25 and 26 so that the end of the rivet 23 may be made flush with the bottom surfaceof the strip 14. Therefore, there is-no-tendency forthe'rivet 15 to catch upon the ciorrugations oftube 11 as the guide is flexed. The strip Isis provided with a longitudinal slot 27 the center of whichis inrcgister with the hole v24. As shownin Fig.5, the'free end of the strip 14 may be slightly upturned as shown at 28 so that this 'end will not catch in the corrugations of tube '11. The free end of strip 14 may also be tapered, the beginning of this-taper being shown .at 29 in Fig. 3.

The bottom face of the tube 11 is provided With similar strips Bland 32 which are similarly secured to each other and to the flanges 12 and 13. v

A'model constructed in accordance with "Fig. 3-utilized 6"w1ength of seamless corrugated waveguide having min imum internal dimensions of 0.4" by 0.9 with standard coupling flanges afiixed to the ends. Strips '14, 15, 31 and 32 were of beryllium copper approximately .OflO thick and approximately the width of the outer face of the tube 11. When the model was flexed, the strips bent uniformly following approximately the arcs of circles the radii of which decreased as the guide-was flexed further. The strips pressed against'the tube 11, causing it to assume the same smooth curve as the strips with no sharp bends. The guide was tested with bends of 90 in each direction (180 total) with no measurable changein the voltage standing wave ratio throughout this range.

It isapparent that a guide constructed in accordance with the invention maybe easilypressurized and will operate satisfactorily over a wide range of ambient temperatures since there is no rubber to become soft at high temperatures and 'brittle at low temperatures.

The slots such as 27 in the strip *15 may be made of such a length that the rivets bear against the end of the slot when the guide has been flexed a predetermined amount, such as 90". This prevents maltreatment of'the guide by persons not familiar with 'its limitations.

Referring now to Fig. 6, there are shown two strips 41 and 42 comparable to the strips 14 and 15 'of Pig. 3. As in the case of Fig. 3, the upper strip 42 i s provided with a longitudinal slot 43. The lower strip 41 is provided with a transverse slot 44 the center of which is inregister with the center of slot 43'. The strips are fastened together by means of a rivet 45 in a manner similar to that shown in Figs. 4 and 5. Although only one rivet is shown in Fig. 6, it-will be understood that the strips 41 and 42 are fastened near each end, as in Fig. 3. The double slot arrangement of Fig. 6 allows limited movement at right angles to the principal movement. If the strips 41 and 42 are placed along the broad face of a guide, the principal movement will be in the E plane while limited movement in the Hplane is also possible.

Figs. 7 and 8 show another means for fastening two strips together. In Fig. 7 there is shown a strip 46 the end of which is tapered to form a narrow'portion 47 and is then widened to form "a key :portion 48. Near the opposite end of strip 46, there is cut through this strip a keyshaped portion49. The strip 46 is usedin conjunction witha strip 51 as shownin Fig. 8. The strip 51 is provided withtwo slots 52 and 53 similar to the slots shown in .Fig. 3. When the apparatus is assembled, the keys '48 and 49 of the strip 46 are bent up, twisted 90, inserted through the slots v52 and 53 and twisted back their original shape. The fastening action is similar tothat of the rivets '22 and 24 of Fig. 3.

Fig. 9 shows another arrangement of strips which may be used. In this embodiment'tworesilientstrips 56 and 57 are provided, each of which is slightly less than half thewidth of the face of the guide. These strips are laid side by side along the top of the guide. Near thatend of'strip' 56 which is secured to the flange, a narrow strap of relatively rigid material 58 is secured, for example, by means of a rivet 59. The strap 58 extends transversely strap 61 is secured by means of a rivet 62. Strap 61 extends transversely and overlies the strip 59 without being fastened to it. It is apparent that as the guide is flexed, the strip 56 and 57 may slide longitudinally with respect to each other and to theguid'e, while the straps 58 and 61 will hold the strips 56 and 57 in contact with the face of the guide.

The "invention has been described with respect to a numherof specific embodiments. However, many modifications may be made within the scope of the invention. For example, the strips 14 and 15 may be secured to the flanges or to the ends of the guide in any desired manner. Many other modifications will occur .to those skilled in the art.

What is claimed is:

1. A flexible waveguide comprising, a conductive tube having transverse corrugations, a first resilient strip lying along the outside of said tube and rigidly secured to one end thereof, a second resilient strip adjacent to said first strip and rigidly secured to the other end of said tube, and means forfastening said strips together so as to permit relative longitudinal motion and restrain relative motion normal to the planes of said strips.

2. A flexible waveguide comprising, a seamless, hollow, conductive tube of generally rectangular cross section having transverse corrugations to render said tube flexible, a flange secured to each end of said tube for coupling said tube to other microwave'components, a first resilient metal strip lying along one face of said tube and rigidly secured to one ofsaid flanges, a second resilient-metal strip overlying said first strip and rigidly secured to the other of said flanges, means for holding adjacent faces of said strips in contact while permitting relative longitudinal movement of said strips, and third and fourth strips, similar to said first and second strips and similarly arranged and secured,lying along the opposite face of said tube.

3. A flexible waveguide comprising, a seamless, hollow conductive tube of generally rectangular cross section having transverse corrugations to render said tube flexible, a flange secured to each end of said tube to adapt said tube for coupling to other microwave components, a first resilient metal strip lying along one face of said tube and secured to one of said flanges and having two holes, one near one end and one near the other end, a second resilient metal strip overlying said first strip and secured to the other of said flanges, said second strip having two longitudinal slots, one near one end and the other near the other end, the holes in said first strip registering with the center of the slots in said second strip, a pair of rivets loosely securing said strips together, one rivet passing through one hole and slot and the other rivet passing through the other hole and slot, whereby the adjacent faces of said strings are held together while relative longitudinal motion of said .strips is permitted, and third and fourth strips similar to said first and second strips and similarly arranged and secured, lying along the oppositeface of said tube.

4. A waveguide comprising a flexible, conductive tube, a first resilient strip lying along the outer surface of said tube, a second resilient strip partially overlying said first strip, first means for fastening one end of said first strip to an intermediate portion of said secondstrip, and second means for fastening one end of said second strip to an intermediate portion of said first strip, both said first and second means allowing relative longitudinal movement of said strips while restraining relative motion normal to the surfaces of said strips.

References Cited in the file of this patent UNITED STATES PATENTS 384,352 Emery June .12, 1888 622,706 Nutt Apr. 11, 1.899

(Other-references on following page) UNITED STATES PATENTS Fortune July 10, 1928 6 Weitz Sept. 2, 1930 Powell Sept. 5, 1939 Candee Aug. 7, 1951 FOREIGN PATENTS Great Britain Apr. 30, 1913 

